This grant responds to "NIH Announces the Availability of Recovery Act Funds for Competitive Revision Applications" (NOT-OD-09-058). We propose a novel yet hypothesis-based approach to examine sex differences in stress responsivity and addiction using established procedures. Stress responsivity relates to acquisition of drug self-administration, a model of addiction vulnerability, and both shows sex differences. Links between maternal care and stress responsivity of offspring are established;greater care relates to lower stress responsivity in adults. Further, these effects are mediated via epigenetic mechanisms. Maternal care differs by pup sex;males receive more care than females. Consistent with the link of maternal care with stress responsivity, adult males show lower stress responsivity than females. We hypothesize that sex-dependent maternal care influences sex differences in stress responsivity and cocaine self-administration reflecting altered DNA methylation of specific genes (e.g., Gr17, Bdnf) in select brain areas (e.g., NAc, PFC, and hippocampus). We will test this by manipulating maternal care via altering litter gender composition (LGC;single- vs mixed-sex litters). LGC influences stress responsivity in infant mice and juvenile and maternal behaviors in rats and mice. Both male and female adult rats of single-sex litters are predicted to show lower stress responsivity than offspring of mixed-sex litters. In Specific Aim 1, we will confirm prior studies demonstrating sex-specific effects of maternal care. We will measure stress hormone levels to stressors and assess glucocorticoid feedback sensitivity. We predict the following effects of LGC on stress responses: mixed females>single females >=mixed males>single males. The relationship between stress responsivity and drug self-administration is complex and may be non-linear;both low and high stress responsivity may associate with low responding. Thus, we predict LGC will attenuate cocaine self-administration in mixed females and single males resulting in an inverted U-shaped function of stress responsivity to cocaine self-administration. Studies in Specific Aim 2 will test effects of LGC on acquisition of cocaine self-administration and food responding. Specific Aim 3 will address epigenetic contributions to these sex differences by assessing DNA methylation patterns of targeted genes in brain regions associated with stress responsivity and drug self-administration. Data will inform on the role of maternal care and underlying epigenetic mechanisms that contribute to sex differences in stress responsivity and addiction. PUBLIC HEALTH RELEVANCE: The goal of this research is to achieve a better understanding of sex differences in stress responsivity and vulnerability to addiction. Studies in this competitive revision will test the hypothesis that these sex differences are due to sex-dependent differences in maternal care received and reflect epigenetic effects of targeted genes in select brain regions.